Studies are in progress which are designed to elucidate the molecular and cellular mechanisms which regulate hemopoietic cell differentiation in the human and experimental animal. Specific objectives include the study of regulatory defects in inherited disorders of hemopoietic development in man and studies on the effects of erythropoietin on cell differentiation in vitro. BIBLIOGRAPHIC REFERENCES: Terada, M., Friend, J., Nudel, U., Rifkind, R. A., and Marks, P. A. Transient inhibition of initiation of S-phase associated with induction of murine erythroleukemia cells to erythroid differentiation by dimethylsulfoxide. Proc. Nat'l. Acad. Sci., U.S.A., 74(1), p. 248-252, 1977. Fibach, E., Reuben, R. C., Rifkind, R. A., Marks, P. A. Effect of hexamethylene bisacetamide on the commitment to differentiation of murine erythroleukemia cells. Cancer Research, 37:440-444, 1977.